The present invention relates to wheelchairs, and particularly to wheelchairs capable of moving the seat and back for tilting and reclining.
Wheelchairs often have a fixed seat consisting of a seating surface and a back frame. The seating surface is usually either horizontal or slightly tilted back, with the front edge of the seating surface slightly higher than the rear edge of that surface. If the wheelchair user sits in the same position in a wheelchair for a long period of time, pressure is continuously applied to the tissue on the portion of the user""s body (buttocks, legs, and/or back) that is bearing the user""s weight in that position. Blood circulation to that tissue will be reduced, and ulcers or other problems can result.
To avoid these problems, it is necessary for people sitting in wheelchairs to shift their body weight from time to time. This is often accomplished by tilting the seat portion of the wheelchair backwards so that the user""s weight is shifted away from the pressure points on the user""s body. Also, the user""s weight can be shifted by reclining the back frame.
A problem with wheelchairs that have both a tilt and recline capability is that the user""s body is subject to shear problems during the maneuvering of the tilt and the recline apparatus. Due to the displacement between the anatomical pivot of the hip and the seat/back pivot, shear forces are introduced in the recline process. Previous efforts to mitigate this shear force have resulted in only crude approximations of the correct location of the back. Another problem seen in existing recline chairs is a tendency of the individual to slide out of the seat after repeated reclines. This can be due to the shear forces. Also the way the hip rotates during the recline process can be different from how it rotates when the individual comes back up or unreclines.
It would be advantageous if there could be developed a wheelchair having a tilt apparatus and a recline apparatus, where the tilt and recline functions are operated to minimize the shear forces transmitted to the wheelchair user. Also, it would be advantageous if there could be developed a method of unreclining, i.e., returning the reclined backrest of a wheelchair to an upright position, without causing the wheelchair user to have a tendency to slide forward along the wheelchair seat. Further, there is a need for improvements in wheelchairs to make them more conformable to the user""s needs.
The above objects as well as other objects not specifically enumerated are achieved by a wheelchair having a base and further comprising a seat frame mounted for tilting with respect to the base, and a seat frame tilting mechanism for rotating the seat frame with respect to the base. A back frame is mounted for reclining with respect to the base, and a back frame recline mechanism is positioned for rotating the back frame with respect to the base. A controller is provided for separately controlling the seat frame tilting mechanism and back frame recline mechanism so that the seat frame and the back frame can be rotated independently.
According to this invention there is also provided a wheelchair having shear reducing characteristics. The wheelchair includes a wheelchair base, a back frame mounted for reclining relative to the base at various angles of recline with respect to an initial position, a shear plate mounted on the back frame for movement with respect to the back frame, and a counter weight mounted on the back frame and connected to the shear plate so that the shear plate is counterbalanced, thereby enabling the shear plate to be freely moved with respect to the back frame to reduce the shear experienced by users of the wheelchair.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.